We propose new methodology based on chemical labeling and mass spectrometry (MS) for the discovery and qualitative analysis of unknown DNA adducts in human samples. Novel, bulky, nonpolar cationic reagents will be synthesized and tested as labeling reagents for both nucleotide and nucleoside versions of DNA adducts. The primary purpose of the chemical labeling is to make all DNA adducts highly and equally (or near so) sensitive for analysis by MS. Especially laser desorption (including MALDI) but also electrospray forms of MS will be used. In the former case, large spot laser desorption on a Fourier transform mass spectrometer (FTMS) will be emphasized. The project is stimulated in part by our unpublished observation that bulky, nonpolar compounds that we have prepared are very sensitive by MALDI-MS. Potentially a DNA adduct labeled with a reagent of this type also can be detected with high sensitivity. If this can be demonstrated in an R21, then the ensuing R33 would involve further optimization of the technique, with eventual application in the project to DNA extracted from large, autopsy, human tissue samples to bring the overall methodology to full maturity.